Here's some more wavelets on TD15 impulse response posted earlier. This is the "full damping" case. There are three transforms of different wavelet lengths of 1ms, 2ms and 5ms. These are non-normalised so amplitude information is true. Also notice that the frequency axes have different scales.

From 1ms wavelet one can see energy is packed at 2.5ms. But there are things happening before 2ms also.

In 5ms wavelet the direct sound and the energy at 2.5ms are overlapping and comb filtering occurs. These is mostly visible at 2ms and between 2-4kHz.

It seems clear to me that the energy at 2.5ms is cabinet reflections/diffractions. Maybe that was obvious already

I don't know what is your position but nothing you have said so far changes the fact that "frequency response" indicates system's response at steady state. This is what I said in the beginning and you opposed.

- Elias

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Originally Posted by JohnPM

In the limit an infinitesimally short sweep is an impulse, and I think we know the term used for the output of a system when driven by an impulse. Perhaps you are aware that sweeps are also referred to as "time stretched pulses", particularly amongst Japanese researchers, and the motivation for their use is to spread the energy of the impulse out in time so that the total energy delivered is far greater than the system could cope with if an impulse were used directly. Or perhaps not.

One measurement I would like to see is to place the two enclosures back to back and feed the signal only to the front one as before. This would propably remove the diffraction at 2.5ms and place it further in time domain. Just to validate (by direct comparision) that the 2.5ms really is from the cabinet.

Elias my tests of the AE drivers were on an open baffle, so there was no rear wall reflection.

From John J's comments I take it that this is a suspension or cone issue. It is not as noticeable with the fabric surrounds, although it is still there. It is also most noticeable on the 15" drivers. My guess is it is cone/surround interface issue. Similar to the dip you see around 800-1000hz, on smaller drivers, especially 8" woofers for whatever reason. Or cone flex issue that is mitigated by fabric surrounds but not helped by foam surrounds.

Anyway I haven't seen any big woofers with better IR than the AE drivers so not sure what the fuss is about.

Elias my tests of the AE drivers were on an open baffle, so there was no rear wall reflection.

Same here. I tested without the cabinet, and the 2.5 ms wrinkle was still there.

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Anyway I haven't seen any big woofers with better IR than the AE drivers so not sure what the fuss is about.

My feelings exactly! Judging by the results, I'm pretty sure that Nick McKinney worked hard to chase out every problem he could while developing this driver.

All of the 15" drivers I have used have brought a certain quality (solidity, authority) to the presentation that I really like. As with everything else in speaker design, there are compromises as well. The TD15M doesn't measure as cleanly as the little Vifa drivers in the Ariel, but its strengths are obviously different.

As much as I have liked the other 15" drivers I have used (Altec 416, 515, 604, Klipsch K-48), I don't expect the TD15M will be a disappointment.

Of course I am curious about the cause of the 2.5 ms ripple, but I have less than two weeks remaining before starting back to work, and need to focus on completing the crossovers.

I was under the impression that there was no intension to tweek the driver.

Gary did say he was not interested in modifying the driver. However, if simple reversible damping could be applied to the spider (assuming that's indeed the source of the reflection/resonance), then he or others might try it. But not much point until it's determined that the phenomenon is an audible issue in the given application. I have 15" Lambda TDX (Apollo motor) in my system. Since I cross them around 400Hz, I'm not much motivated to experiment. John at AE might be interested in mitigating this issue, especially since these drivers do have extended frequency response.

I don't know what is your position but nothing you have said so far changes the fact that "frequency response" indicates system's response at steady state. This is what I said in the beginning and you opposed.

Elias, without in any way wishing to appear rude, that is a meaningless statement. The system's frequency response and impulse response are interchangeable, they both describe the same system and how it affects signals that pass through it. Would your statement make sense to you if it read "the impulse response indicates the system's response at steady state"? There seems to be a continual confusion between the system's frequency response, which is an invariant property of the system, and the spectrum of the system's output and/or the spectrum of segments of the system's impulse response as it evolves over time. They are not the same thing.

Nice to see where your misunderstanding has come from Elias, but unfortunately you have things back to front. The response to a sinusoid, just like the response to any input, is determined by the frequency response (including the transient behaviour). The frequency response is not determined by hanging around for the transients of applying an infinity of sinusoids to decay.